UKC

Just topped up my tyre pressures and on checking the hand book found I've over inflated by up to 3 psi.

Is this small "over inflation" likely to make much difference or is it worth deflating them a little?

In reply to FesteringSore:

Depending on the gauge, I'd be surprised if it was accurate to 3psi. If the tyre is in the sun, or is warm, again I'd expect the pressure to be slightly higher than when cold.

Personally I think I'd find something more important to worry about than 3psi. In always topping up my car tyres as the alloys are corroded and leak a little.

In reply to FesteringSore:

3 psi extra is enough to cause the tyre to wear more in the middle than the edges.

However most makers recommend a range of pressure dep on speed you are driving at, weight of car, passengers & contents & in our family Astra's for eco running.

In reply to FesteringSore:

3 psi will definitely make a difference. Some cars it makes a noticeable difference to handling as well as tyre wear. Go to manufacturers specifications and then alter slightly from there if needed for wear/grip issues.

In reply to FesteringSore:


Yes you're going to die!!!!!!!!!!!!!!!!!!!!!!!

And even if you let it out it's too late now, there like condoms (once they're stretched they don't go back), you'll have to buy four new tyres to ensure your future safety.

In reply to FesteringSore:

Under inflation is more a problem than over inflation within reason as it causes excess flexing of the side walls which could cause a sudden blow-out. Most cars have a range of recommended pressures depending on the loading.

In reply to FesteringSore:

If you like to drive your car like you stole it then increased pressures (2-3psi) can help apparently - the extra stiffness helps cornering.

In reply to solostoke:


Yes, but most people won't notice this change in tyre response. For 'normal' people driving on the road it won't make much difference unless the tyres are cheap and useless to start with. 3psi is enough to make a noticable difference to fuel economy on a long drive though. On cars with a fair amount of camber, an extra 3psi would also be enough to increase the rate of tyre wear on the inside shoulder. Rear tyres on BMWs and Minis for example.

In reply to krikoman:


You're able to stretch condoms? Oooeerrrr missus.
(won't mention the 'there' they're' slip up )

In reply to graeme jackson:


I don't like the sound of condoms and slip ups in the same sentence, it reminds me too much of my ex.

In reply to Richard Wilson:

Sometimes quite a large range. On my Land Rover Defender 110:

Front: 30psi
Rear light load: 48psi
Rear heavy load/towing: 65psi

The latter is over double the former on exactly the same tyres.

In reply to FesteringSore:
I'm experimenting with lower pressures in my tyres at the moment - I know the theory is that lower pressure gives you more grip in the corners, but does it increase the drag on climbs. Plus it feels different to what I'm used to, so it can be a bit unsettling.

Oh hold on, are you talking cars not mountain bikes ? Kick the tyres once in a while, that's about it

In reply to Chris the Tall:


Indeed. OP never specified if he was talking cars, bikes, wheelbarrows or light aircraft....

In reply to FesteringSore:
3 psi over may help with tyre wear. Manufacturers recommend a safe, but not economical pressure. The rec pressure is in the middle of the safe range, which can be affected by many things, eg load, temperature, and accuracy of measuring device. 3 psi over, on most cars will cause more even wear across the tyre (Look at tyres that have run at the correct pressure for a long time and they will be worn on the shoulders.) The small increase in diameter will also help fuel economy but not by much. On most cars having the whole tread surface in full contact with the road more than offsets any cornering loss due to increased stiffness in the walls at slightly higher pressures.
On the other hand, from the above, don't worry, as long as the pressures are somewhere close, unless you are going to race very hard around corners, or are very picky about fuel and wear economy.

In reply to Neil Williams:






You have to watchout as some tyres are not rated for the high pressures.

In reply to Richard Wilson:

These are, they are the stock ones. Good point though - it is unusually high for a car.

In reply to FesteringSore:
Over-inflation can be more of a problem for modern low and wide profiles because it is then difficult for the tyre to maintain contact with the road surface across the full width of the tyre during the full range of suspension movements. Parts of the tyre will experience more wear as a result.

If the tyre is at the top limit of the pressure for the current load then you might expect the tyre to generate less rolling resistance and thus improve fuel consumption. However, the best of modern tyres work well across a wider range.

Lower tyre pressures can be expected to use more fuel. There may also be excessive wear but on different parts of the tyre. The tyre will generate more heat as it undergoes greater deformations when rotating and this also increases tread wear and can damage the structure. In extreme cases of a heavily laden car with low tyre pressures on a hot day undergoing heavy cornering, parts of the tread will be close to melting and wear very badly.

If some tyres are low and some are high then expect the car's handling to change. This is more likely to be a bad change than a good change.

An important time to check tyre pressures is when the weather changes. During a very cold spell, the air will contract and the pressures will drop. Likewise, during a heatwave it will expand and the pressures will rise.

Recommended tyre pressures are for cool tyres that have not been in direct sunlight or been heated by driving. That's why you need your own tyre pressure gauge so that you can chose to check them at an appropriate time.

So what do you do if you are driving down the motorway 250 miles from home and you think the tyre pressures might not be right. Well, they'll be higher than the recommended value after all that high speed use but they should be very close to the same on both sides. If any of the pressures are lower than the recommended value after motorway use then there's a problem.

If your car has a different tyre size from the maker's recommended size then if it has a larger volume it needs less pressure to support the same weight. Only a little bit: maybe 0.2 bar or 2 to 3 psi. Remember than wider tyres with very low profiles on bigger rims may not actually have a larger volume!